net: __skb_flow_dissect() must cap its return value

After Tom patch, thoff field could point past the end of the buffer, this could fool some callers. If an skb was provided, skb->len should be the upper limit. If not, hlen is supposed to be the upper limit. Fixes: a6e544b ("flow_dissector: Jump to exit code in __skb_flow_dissect") Signed-off-by: Eric Dumazet <[email protected]> Reported-by: Yibin Yang <[email protected] Acked-by: Alexander Duyck <[email protected]> Acked-by: Willem de Bruijn <[email protected]> Acked-by: Alexei Starovoitov <[email protected]> Signed-off-by: David S. Miller <[email protected]>
hardkernel · Nov 13, 2016 · 34fad54 · 34fad54
1 parent 79774d6
commit 34fad54
Showing 1 changed file with 8 additions and 3 deletions.
diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c
@@ -122,7 +122,7 @@ bool __skb_flow_dissect(const struct sk_buff *skb,
 	struct flow_dissector_key_keyid *key_keyid;
 	bool skip_vlan = false;
 	u8 ip_proto = 0;
-	bool ret = false;
+	bool ret;
 
 	if (!data) {
 		data = skb->data;
@@ -549,12 +549,17 @@ bool __skb_flow_dissect(const struct sk_buff *skb,
 out_good:
 	ret = true;
 
-out_bad:
+	key_control->thoff = (u16)nhoff;
+out:
 	key_basic->n_proto = proto;
 	key_basic->ip_proto = ip_proto;
-	key_control->thoff = (u16)nhoff;
 
 	return ret;
+
+out_bad:
+	ret = false;
+	key_control->thoff = min_t(u16, nhoff, skb ? skb->len : hlen);
+	goto out;
 }
 EXPORT_SYMBOL(__skb_flow_dissect);